Fading elimination



Feb. 9, 1937.

H, H. BEVERAGE ET AL. 2,069,813

FADING ELIMINATION Original Filed March 15, 1928 .Fl I 1 I 6' 73REgE/VL-R AMPL war I & 77 9 RECE/VE'R AMPZ/F/ER Fl g v 2 I 43 /5l/VTERl/[fiMTf RECE/VER FRZ-"Ol/Z-WCY AMPZ/F/ER w 49 if Rico/205kATTORNEY Patented Feb. 9, 1937 UNITED STATES PATENT orrle f FADINGELIIWINATION Original application March 15, 1928, Serial No. 261,738.Divided and this application February 10, 1936, Serial No. 63,132

12 Claims.

The invention relates to the elimination of what is commonly known asfading in wireless or radio signalling. It is particularly adapted foruse in the reception and transmission of short wave signals, especiallyin locations where fading conditions are particularly troublesome.

This application is a division of our copending application, Serial No.261,738, which was filed on March 15, 1928.

We have found that signals picked up on antennae located at differentpoints have different fading characteristics, and that where short waveantennae are located at separated points that the signals might be of amaximum intensity at any particular instant on an antenna located at onepoint and at the same instant be of a minimum intensity on an antennalocated at another point. In order to combine the signals received onthe various antennae which are, as above stated, geographicallyseparated with respect to each other, the first thought was to carry theradio frequency energy pickedup on the various antenna systems inquestion to some common receiver and to add the separate energiesdirectly together at the common combining point. This, however, has itslimitations because it has been found that the phase relationshipbetween the signal voltage received at one antenna and the signalvoltage received upon another antenna geographically separated from thefirst antenna does not remain fixed but changes from moment to moment.Therefore, it is relatively ineffectual to provide an arrangement fordirectly combining the radio frequency voltage from the plurality ofantenna systems located at various geographically separated points sincethese voltages might add at one instant and subtract at another instant,due to the fact that the radio frequency voltages from the variousantennae will not always be in phase. 7

. t is, therefore, an object of our invention to provide a method andmeans of combining signals from various geographically separatedantennae independent of the phase relationship of the signals asreceived on the various antennae.

The broad idea of combining signals from various geographicallyseparated antennae has been disclosed in our U. S. Patent 1,819,589,issued August 18, 1931.

Referring to the accompanying drawing, Fig. 1 illustrates an arrangementfor combining signals in a receiving circuit independently of theirrelative phase; and

Fig. 2 illustrates a modification of Fig. 1.

.In Fig. 1 we have shown a method for liminating short wave fading inwhich the audio frequency outputs of two geographically separated radioreceiving systems are addedwRadiofrequency energy of the desired signalis picked up on two geographically separated antenna systems, I and 3,which carry their respective energies to receiving systems of anydesired character and 1. Associated with the receiving systems 5 and 1are two separate local oscillators 9 and II, there being one oscillatorfor each receiver system. These oscillators are used to heterodyne theincoming signal energy as received upon the geographically spacedantennae l and 3. In each receiving system 5 and I, which are intendedto include the usual detector circuits, the outputs of the detectorsarefed through-any desired form of leads to amplifiers l3 and I5. Theoutputs of amplifiers l3 and 15 are impressed upon the primary windingsl9 and 2| of the transformer I! from which the energy is transferred tothe secondary winding 23. Included in the'secondary circuit 23 are a setof phones or any other type of receiving unit or translating device 25.

It will be noted from the above that there is one primary winding H9 or2| for each receiving system l or 3 and that the secondary winding 23 ofthe transformer ll contains two different frequencies from the twodifferent receiving systems. The heterodyne oscillator 9 which iscoupled with receiving system 5 is preferably so adjusted that the beatnote resulting may be of the order of 800 cycles. The oscillator whichis coupled with the receiving system I is preferably so adjusted thatthe beat note resulting may be of'a frequency of 1,000 cycles, althoughit is to be understood that we can successfully use beat frequenciesother than those which we have mentioned. It is thus seen that there isan 800 cycle output from receiving system 5 and al, 000 cycle outputfrom receiving system I. These two frequencies which will now be denotedby F1 and F2, respectively, are passed through the two primary windingsl9 and 2| respectively of the output transformer l1 and both frequenciesappear in the secondary winding 23 which is connected with the receivinginstrumentality such as the phones 25.

If an operator is listening in the phone 25, he may note that in oneinstant the 800 cycle note I or frequency F1 at one time predominates,due to the factthat the energy picked up by the antenna system I whichis connected to this receiver is greater than the energy picked up bythe antennasystem 3 connected with receiving 'pr-eciable length of time.

system 1. However, at another instant it might appear to be that the1,000 cycle note, or frequency F2 will predominate in the phone 25, dueto the fact that the energy. picked up by the second antenna system 3 isnow greater than that picked up by the-antenna system of the firstreceiver 5. q

It is thus seen that there are two different frequencies in thesecondary of the transformer l1 oscillators 'as'has been abovedescribed, to produce twqdifferent audio frequency outputs, anarrangement can be established where the audio frequency outputs inanoutput transformer are arranged ,to, obtain satisfactory reception sinceone beat note will predominate at one instant and "another beatnote willpredominate at another instant, but at all times whenany signals reachantenna or 3 the operator will have a signal inphones 25.

It is thus seen'that We have produced by this arrangement a methodandapparatus which will effectively eliminate the efiect of fading bycombining the signals received on each of the two or more geographicallyseparated antenna systems independently of the phase relationship.

From the above description it is obvious that the same method andprinciple may be used ,tocombinethe outputs of morethantwo antennae.Thus,'to combine the outputs from n antennae, in accordancefwith theprinciple above set forth, n receivers would be used and produce ndifferent frequency outputs which would all add theirenergiestogether inthe common receiving instrumentality, as for example; the phones 25.

As also will be understood from a reading of the above description itwill be noted that the speed of signalling is practically a function ofthe frequencies transferred to the receiving instrumentality. Therefore,if it is necessary to increase'the speed of signalling to any greatextent itis advisable to substitute two low radio frequencies for thefrequencies referred to above as F1 and F2. I g V In order to adapt thesystem shownby Fig. 1

'to higher signalling speeds, it isdesirable to modify the showing ofFig. 1 to operate with low radiofrequencies for F1 and F2. Fig. 2 showsa suitable form for such a'modification. Referring now to Fig. 2antennae3| and 33 are coupled to transmission'lines 39 and 4| by suitable means,such as transformers 35' and. 31.

45* respectively. Each of the receivers-43 and 45 heterodyne thereceived signal to a lower frequency, either'by autodyne reception, orby using separate oscillators 4| and 49. For exampla oscillator 49 maybeadjusted to produce a'beat frequency F1 of 40,000 cycles, andoscillator49fmay'be adjusted to produce a beat frequency F2 of 42,000cycles on the same signal. The outputsof receivers 43 and 45 are con.-nected in ai'suita'ble'manner to an intermediate frequency amplifier 5|;which amplifies F1. and

V The transmission lines 39'and 4| terminate at receivers 43 and F2equally, but is selective enough to exclude undesirable frequencieslying outside of the 40,000 to- 42,000 cycle band.

Amplifier 5| is connected to the primary 53 of transformer 55. Thesecondary 51 of this transformer 55 is associated with a full waverectifier consisting of devices 59 and 6|. The rectified current outputof the rectifiers 59 and BI is ar- ..ranged to operate a recorder orother suitable receiving instrumentality 65. Connected across the outputof the rectifier for the purpose of suppressing the beat frequencybetween F1 and F2, while allowing the relatively low frequency keyingimpulses to pass is a capacity element 63. In the example cited, whereF1 has been chosen, for example, as 40,000-cycles and F2 as 42,000cycles,

the beat note will'be (F2F1) or 2000 cycles, and I with a full'waverectifier, this would largely appear as the second harmonic, or 4000cycles. The

keying pulses have a fundamental frequency of about 40 cyclesper secondfora Morse-code speed of 100 words ;per minute. [Hence it will be seenthat the capacity 63 will have 100 times ,more

shunting effect on the combination frequency than on the keyingfrequency in the example cited. If greater speeds'of transmission aredesirable,-condenser 63 could be replaced by a'low pass filter, whichwould pass high speed keying impulses, but would entirely suppress thecombination frequencies.

While Fig. 2 and the description pertaining thereto has been illustratedby showing two antennae and assuming a frequency difference of 2000cycles, it is to be understood that several antennae could be combinedby utilizing-more receivers and combining the outputs of these receiversin a suitable intermediate frequency amplifierwith suitable spacingbetween'the different heterodyne frequencies.

The principles involved in Fig. 2 are fundamentally the same as in Fig.1, excepting that a receiving instrumentality has been substituted whichwillbe operative over a wider band. of frequencies. than the phonesof 1. frequenciesFi, F2; F3, etc. arediiferent, the phase relationsbetween them change at avery-high rate as compared withboth the rate offading and the rate of keying. Therefore, it is possible to suppress thecombination frequencies without interfering with the keying pulses,ashas already been explained. Hence, it is seen that changes Sincethe inradio frequency signal phase between the several'antennae, have noeffect on the final rectified output, and'that the energies are added inthe recorder irrespective of phase relations.

This results in a final signal output-relatively free from fading at thereceiving instrumentality,

provided that-the several antennae have been located for suitable fadingdiversity. 'We have found that a spacing on the order of 1000 feetbetween antennae gives excellent diversity on short Wave signal fading,for example, onwave lengths up to at least 30 meters.

We claim:

'1. The method of receiving wireless signals with geographically spacedantenna systems which comprises receiving, the same signal upon each ofa-pair of geographically lseparated'antenna systems and producing a pairof signal effects therefrom, producing in each of said receiving systemsassociated with said geographically spaced antenna systems a beat noteof different.

frequency, combining and then rectifying the separate beat notesfromeach of said antenna:sys-' temsin a receiving circuit whereby theseparate signal energies are combined independently of their relativephase relationship and the effects of fading are substantiallyeliminated.

2. The method of receiving wireless signals with geographically spacedaerials which comprises, receiving the same signal upon each of a pairof geographically separated aerialsand associated receiving systems forproducing a pair of signal effects therein, introducings'eparate'frequency energy in each of said receiving systems forproducing a beat note of dififerent characteristics in each of saidreceiving systems, combining and then rectifying the said beat notesproduced in a combining circuit whereby the signals received upon eachof said geographically separated receiving systems may be combinedindependently of the phase relationship of the signals reaching the sameand the effects of fading substantially reduced. I

3. The method of receiving wireless signals With geographicallyseparated aerials which comprises, receiving the same signal upon eachof a plurality of geographically separated aerials, and producing aplurality of signal effects thereon directing the energy from each ofsaid aerials to separate receiving systems, introducing into each ofsaid receiving systems a second frequency and producing a beat frequencydiffering in character in each of said receivers, amplifying the beatfrequency produced in each of said systems, combining and thenrectifying the separate beat frequencies in a combining circuit wherebythe effects of fading are substantially eliminated and the signalsreceived upon each of said aerials are combined independently of thephase relationship.

4. An apparatus for the elimination of fading comprising, a pair ofgeographically spaced antennae each adapted to receive the same signaleffect, a receiving system associated with each said antenna, means forproducing beat notes in each of said receiving systems, said beat notesdiffering in frequency in each of said systems, a combining circuit, aresponsive device, and means for so combining and rectifying the beatnotes from each of said systems that the received signals as sensed bysaid responsive device are substantially unaffected by fading and arecombined independently of the phase relationship of the signals reachingsaid antenna.

5. An apparatus for the elimination of fading comprising, a plurality ofgeographically spaced antenna systems for receiving the same signaleffect, a receiving system associated with each of said antennae, anoscillator of different frequency associated with each of said receivingsystems, means for producing a beat note by the action of saidoscillator frequency upon said received signal frequency, meansassociated with each of said receiving systems for combining and thenamplifying the beat notes so produced, a beat frequency detectorresponsive to the combined energy from said amplifying means and meansassociated with said beat frequency detector and so characterized thatupon operation in response to signals simultaneously received by saidplurality of antennae the effects of fading are substantially reducedindependently of the phase relationship of the signals reaching saidantenna systems.

6. An apparatus for the elimination of fading comprising, a plurality ofantennae each having different instantaneous fading characteristics, aseparate receiver associated with each of said antennae, means forproducing difierent output frequencies from said receivers for the samereceived'signals a common selective intermediate frequency amplifier, arectifier coupled with the output of said intermediate frequencyamplifier, a receiving instrumentality associated Withthe output circuitof said rectifier and a condenser shunting said output circuit, wherebysignals received upon said antennae are received in said receivinginstrumentality'substantially unaffected by fading and are combinedindependently 'of the phase relationship of the signal reaching saidantennae. a A

7 An apparatus for the elimination of fading comprising, a plurality ofgeographically spaced antennae each having different instantaneousfading characteristics and each adapted to receive the same signalenergy, a separate receiver associated with each of said antennae, meansfor producing a different radio frequency heterodyne beat note on thesame signal with each receiver, a selective intermediate frequencyamplifier associated with the output of each of said receivers forequally amplifying the separate beat frequencies, a full wave rectifierconnected with the output of said amplifier, a filtering means connectedin the output circuit of said rectifier, and a receiving instrumentalityalso associated with said rectifier in the output cire relatively highfrequency at separated places,

combining said waves received at said places with combining waves offrequency different from that of the received waves to produceintermediate frequency waves of frequency lower than that of saidreceived Waves, the frequency of said combining waves being different atdifferent ones of said places, whereby intermediate frequency waves ofdifferent frequency result from said combining actions, adding saidWaves of intermediate frequency to produce a resultant wave, anddetaching the signal component of the' latter wave as a relatively lowfrequency signal current.

9. The method of reducing fading effects in the reception of radiosignals, which comprises receiving at a plurality of receiving stationsradio signals transmitted from the same transmitting station, beatingthe received signals at each receiving station to an intermediatefrequency, the said intermediate frequency being different for differentones of the receiving stations, transmitting the said intermediatefrequency currents from each receiving station to a common station andcombining and then rectifying at the latter station the saidintermediate frequency currents.

10. In a radio signaling system, the combination of a plurality ofreceiving stations, each having means to receive a signal sent by thesame transmitting station and to beat the received signal to anintermediate frequency, said intermedi ate frequency being different fordifferent ones of the receiving stations, means to combine and thenrectify the intermediate frequency signals of all receiving stations andmeans responsive to the energy so combined andrectified.

11. In a radio signaling system, the combinetion of a plurality ofreceiving stations having means to receive signal waves of the samefrequency, means for supplying combining-oscillations to all receivingstations, said combining oscillations being different for different onesof the receiving stations to'produce with the received signal waves atthe receiving stations intermediate, frequency Waves of differentfrequencies, means to add the intermediate frequency waves from all ofthe stations to produce a resultant 'wave, and means to detect thesignal component of the said resultant wave.

'12. A multiple station radio receiving system comprising a plurality ofseparated radio receiving stations, antenna means at each separatedstation for collecting from the ether a signal modulated wave of highfrequency, means at each of said separated stations for producing,

from said signal-modulated wave of high frequency, signal-modulatedwaves of intermediate frequencyvwhichare different for each station,

' and a singledevice for detecting" the signal corn- 7 ponent of saidwaves.

HAROLD'H. BEVERAGE. HAROLD O. PE'I'ERSON.

